Control valves (e.g., sliding stem valves) are commonly used in process control systems to control the flow of process fluids. A control valve typically includes an actuator (e.g., an electric actuator, a hydraulic actuator, etc.) that automates operation of the control valve. Sliding stem valves such as gate, globe, diaphragm, pinch, and angle valves typically have a valve stem (e.g., a sliding stem) that drives a fluid flow control member (e.g., a valve plug) between an open position and a closed position.
Electric actuators often employ a motor operatively coupled to a flow control member via a drive system (e.g., one or more gears). During operation, when electric power is supplied to the motor, the electric actuator moves the flow control member between a closed position and an open position to regulate fluid flowing through a valve. When the valve is closed, the flow control member is typically configured to sealingly engage an annular or circumferential seal (e.g., a valve seat) disposed within the flow path to prevent the flow of fluid between an inlet and an outlet of the valve.
When the valve is in the closed position and electric power is provided to the motor, the motor typically provides sufficient seat load to the fluid flow control member to ensure that the fluid flow control member is in sealing engagement with a valve seat of the valve. When electric power is removed from the motor, the drive system (e.g., worm gears) may maintain the position of the fluid flow control member relative to the valve seat and prevent substantial movement of the fluid flow control member in a reverse or opposite direction (e.g., away from the valve seat). However, the drive system may not provide an adequate or sufficient seat load to the fluid flow control member to ensure the fluid flow control member is in sealing engagement with the valve seat. As a result, fluid may leak through the valve between the inlet and the outlet of the valve.